The present invention relates to an optical fiber core wire binder comprising a photocurable resin composition and suitable for covering an optical fiber, a solid material formed by using thereof, and an optical fiber unit, such that the formation of bubbles at the interface between a solid material and an optical fiber is suppressed.
An example of an optical fiber unit used in an optical submarine cable or the like is shown in FIG. 1. FIG. 1 is a cross section, wherein 1 indicates a center tensile wire, 2 indicates multiple optical fiber core wires twisted together around the center tensile wire 1, 3 indicates an inner layer unit solid material filled between the optical fiber core wires, to protect them, and 4 indicates an outer layer unit solid material. 5 indicates an optical fiber unit thus constituted. Here, the outer layer unit solid material 4 is made of a relatively hard resin, to protect the optical fiber core wires from external force, and the inner layer unit solid material 3 is made of a relatively soft UV resin, to protect the optical fiber core wires 2 by alleviating external force. Generally, since photocurable resins have the advantage that they cure quickly and are good in productivity, they are used as resins for solid materials of optical fiber units. This optical fiber unit 5 is used, for example, as a core of an optical submarine cable, as shown in FIG. 3.
FIG. 3 is a cross section, wherein 11 indicates an optical fiber unit (the same as shown in FIG. 1), which is held in a composite metal body composed of an iron three-section pipe 12, a tensile piano wire 13, and a copper tube 14. A waterproofing resin 15 is filled between the optical fiber unit 11 and the iron three-section pipe 12, and between the tensile piano wires 13. 16 indicates an insulating layer, and 17 indicates a corrosion-preventive layer (jacket). 18 indicates an optical submarine cable thus constituted. The above metal composite body also functions as a feeder for repeaters or the like.
In the meantime, in the production of this optical fiber unit, while multiple optical fiber core wires 2 are being twisted together around a center tensile wire 1, a photocurable resin is filled into the spaces between the optical fiber core wires, to cover the optical fibers. At that time there arises the problem that tiny bubbles inevitably remain in the covering layer of the solid material made of the cured resin on the optical fiber core wire side since the twisting is carried out with involvement of bubbles in the photocurable resin. It is known that if a number of such bubbles are present around the optical fiber core wires, it causes an increase in transmission loss due to microbends.
Accordingly, such bubbles have to be prevented from remaining.
Further, in addition to the prevention of bubbles from occurring, this type of optical fiber unit is required to have basic properties: It is required that, when the terminal is processed to take out the optical fiber core wires to be connected to the optical fiber core wires of another optical fiber unit, the optical fiber core wires can be easily removed from respective solid materials constituting the optical fiber unit; that is, the workability must be excellent; and the force required for withdrawing the center tensile wire from the photocurable resin of the solid material must not be decreased.
As a conventionally proposed optical fiber unit, one is described in JP-A-61-14210, wherein multiple optical fiber core wires, each circumference of which is coated with a covering layer, are gathered around a center member and are covered with, as a cushioning medium, an ultraviolet-curable resin composition containing a specified acrylic oligomer and a triacrylate of tris(2-hydroxyethyl)isocyanurate. While this, however, improves the heat and humidity resistance, the elastic coefficient, and the like of the cushioning medium, it does not take the problem of the occurrence of microbends due to the involvement of bubbles into consideration at all.
Further, JP-A-62-47008 describes that multiple optical fibers, each covered with an ultraviolet-curable resin, are directly twisted together, an ultraviolet-curable silicone resin is filled into spaces between a center tensile wire and the multiple optical fibers and spaces between the said multiple optical fibers, and two solid layers of an ultraviolet-curable resin, different in Young""s modulus are formed around them, but the aim here is to improve the heat resistance, thereby preventing transmission loss from increasing, and to increase the basic required property, i.e. the workability to make terminal working easy.
Therefore, an object of the present invention is to provide an optical fiber core wire binder comprising a resin composition for covering an optical fiber that forms a cured product (unit solid material) that involves less bubbles, that has fewer remaining bubbles, and that is excellent in adhesion to a center tensile wire (tension member) and in workability when it is filled and applied around optical fiber core wires while they are being twisted.
Further, another object of the present invention is to provide an optical fiber unit wherein bubbles at the interface between optical fiber core wires and a solid material made of a resin-cured product around them are kept from remaining, and the adhesion between the solid material and a center tensile wire, and the workability, are excellent.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.
The above objects of the present invention have been attained by the following means.
That is, according to the present invention there are provided:
(1) An optical fiber core wire binder, comprising (A) a radical-polymerizable oligomer, (B) a radical-polymerizable monomer, (C) a photopolymerization initiator, and at least one compound selected from the group consisting of (D) modified silicone compounds and (E) nitrogen/sulfur atom-containing compounds, with the content of the compound selected from the group consisting of the said components (D) and (E) being 0.01 to 20% by weight of the total of the components (A) to (E), and with the surface tension being 30 xcexcN/m or less at 23xc2x0 C.;
(2) The optical fiber core wire binder as stated in the above (1), wherein the said component (D) is a modified silicone compound formed by introducing an organic group, other than a lower alkyl group, to the terminals and/or the side chains of a di-lower alkylpolysiloxane (silicone);
(3) The optical fiber core wire binder as stated in the above (2), wherein the said component (D) has a molecular weight of 900 to 100,000 and the modified amount expressed by the following equation is 10 to 95%:
modified amount=(X/Y)xc3x97100 (%)
wherein X represents the total molecular weight of all parts of the modified silicone, except the di-lower alkylpolysiloxane skeleton, and Y represents the molecular weight of the entire modified silicone;
(4) The optical fiber core wire binder as stated in the above (2) or (3), wherein the said component (D) contains, as the modifying groups, at least one group whose total carbon amount is 20 to 5,000 (the total number in the modified silicone compound), of a long-chain polyether group, an alkyl group (except lower alkyl groups), a phenyl group, a methylstyryl group, a higher fatty acid ester group, an alkoxy group, a fluorine-substituted alkyl group, and a fluorine-substituted alkoxy group;
(5) The optical fiber core wire binder as stated in the above (4), wherein component (D) contains, as the long-chain polyether group of the modifying group, a copolymerized group of ethylene oxide and propylene oxide;
(6) The optical fiber core wire binder as stated in any one of the above (1) to (5), wherein component (A) is a radical-polymerizable oligomer with a molecular weight of 500 or more, having, at the terminal, at least one polymerizable unsaturated group selected from the group consisting of vinyl groups, acryl groups, and methacryl groups;
(7) The optical fiber core wire binder as stated in any one of the above (1) to (6), wherein component (A) is at least one radical-polymerizable oligomer selected from the group consisting of urethane acrylates, obtained by reacting (a1) a polyol, (a2) a polyisocyanate, and (a3) a compound having a polymerizable unsaturated group and a hydroxyl group at the terminal; epoxy acrylates that are reaction products of a glycidyl ether compound with a carboxylic acid having a polymerizable unsaturated group, such as (meth)acrylic acid; and vinyl ethers;
(8) The optical fiber core wire binder as stated in the above (7), wherein the epoxy acrylates comprise reaction products of a glycidyl ether of a polyol having at least one aromatic ring selected from the group consisting of bisphenols, such as bisphenol A, bisphenol S, and bisphenol F; and phenolic resins, with (meth)acrylic acid;
(9) The optical fiber core wire binder as stated in the above (7), wherein the polyol (a1) constituting the urethane acrylates is selected from among polyols having a molecular weight of 400 to 10,000;
(10) The optical fiber core wire binder as stated in the above (7), wherein the polyisocyanate (a2) is selected from among polyisocyanates having a molecular weight of less than 500;
(11) The optical fiber core wire binder as stated in any one of the above (1) to (6), wherein component (B) is a compound having a structure in which (meth)acrylic acid is bonded to a compound containing a hydroxyl group by esterification reaction;
(12) The optical fiber core wire binder as stated in the above (11), wherein the compound having a structure in which (meth)acrylic acid is bonded to a compound containing a hydroxyl group by esterification reaction is at least one selected from the group consisting of monofunctional vinyl-series monomers comprising phenoxyethyl (meth)acrylate, cyclohexyl (meth)acrylate, nonylphenyloxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, tricyclodecanyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, N-vinyl-2-pyrrolidone, N-vinylpyridine, morpholine (meth)acrylate, N-vinylcaprolactam, and vinylcarbazole, the glass transition point of the homopolymer of each of these monomers being 0xc2x0 C. or more;
(13) The optical fiber core wire binder as stated in the above (11), wherein the compound having a structure in which (meth)acrylic acid is bonded to a compound containing a hydroxyl group by esterification reaction comprises a combination of a monofunctional polymerizable diluent with a polyfunctional polymerizable diluent which is trifunctional or more;
(14) The optical fiber core wire binder as stated in any one of the above (1) to (6), wherein component (C) is at least one, or a mixed system of two or more, selected from the group consisting of 1-hydroxycyclohexyl phenyl ketone, thioxanthone, thioxanthone derivatives, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-l, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide;
(15) The optical fiber core wire binder as stated in any one of the above (1) to (6), wherein the content of component (E) is 0.01 to 10% by weight based on the total amount of the components (A) to (E);
(16) The optical fiber core wire binder as stated in the above (15), wherein compound (E) is at least one nitrogen/sulfur atom-containing compound selected from the group consisting of dithiocarbamates, mercaptobenzothiazoles, mercaptobenzimidazoles, thiuram disulfides, and xanthates;
(17) An optical fiber unit, comprising multiple optical fiber core wires that are gathered to be integrated by means of the optical fiber core wire binder that is a photocurable resin composition as stated in any one of the above (1) to (16), followed by photocuring;
(18) The optical fiber unit as stated in the above (17), wherein the said multiple optical fiber core wires are gathered together with a tensile wire to be integrated by means of the said optical fiber core wire binder, followed by photocuring, and wherein the pull-out strength (withdrawing strength) of the said tensile wire is 5 to 50 N/cm;
(19) The optical fiber unit as stated in the above (18), wherein the tensile wire is made of a metal or has a metal surface; and
(20) The optical fiber unit as stated in any one of the above (17) to (19), wherein the optical fiber unit is a unit for optical submarine cables.